NITRIFICATION IN CHLORAMINATED DRINKING …

1 77th WIOA Victorian water Industry Operations Conference & Exhibition Page No. 42 Bendigo Exhibition Centre, 2 to 4 September, 2014 NITRIFICATION IN CHLORAMINATED DRINKING water SUPPLIES Paper Presented by: Andrew Telfer Author: Andrew Telfer, water Quality Manager, Lend Lease 77th Annual WIOA Victorian water Industry Operations Conference and Exhibition Bendigo Exhibition Centre 2 to 4 September, 2014 77th WIOA Victorian water Industry Operations Conference & Exhibition Page No. 43 Bendigo Exhibition Centre, 2 to 4 September, 2014 NITRIFICATION IN CHLORAMINATED DRINKING water SUPPLIES Andrew Telfer, water Quality Manager, Lend Lease ABSTRACT NITRIFICATION is a known DRINKING water quality issue in CHLORAMINATED systems where ammonia-oxidising bacteria (AOB) feed on free ammonia in DRINKING water , significantly increasing in number producing nitrite which is then used as food by nitrite-oxidising bacteria (NOB) which converts the nitrite to nitrate.

2 NITRIFICATION is a process which can occur rather rapidly and lead to a complete loss of monochloramine residual. There are also a number of different factors which influence the NITRIFICATION process making it a complex issue to understand, control and prevent. Although NITRIFICATION is not an issue with a direct public health impact, it can however, increase water quality risks that may lead to public health concerns. Therefore prevention and early identification of NITRIFICATION is critical. This paper will examine examples of NITRIFICATION , identification of occurrences of NITRIFICATION , and also examples of the implementation of preventative and reactive control measures to manage NITRIFICATION in DRINKING water distribution systems across South Australia and Victoria.

3 INTRODUCTION When I began working in the field of DRINKING water Quality Management, I was warned about NITRIFICATION , the havoc it could cause in terms of loss of chloramine and chlorine residuals. I was also warned that I had to be continually on my guard because it could appear and get out of control quickly. But when I asked questions about how to identify it, no one could give me a definitive answer but just that it involved rapid changes in trends of total chlorine, free ammonia, nitrites and nitrates, and that I would know it when I saw it. Ever since then I have been interested to find out more and understand better the causes of NITRIFICATION and how to prevent it occurring in CHLORAMINATED DRINKING water supply systems.

4 NITRIFICATION is one of the major concerns and risks associated with chloramination of DRINKING water supplies. However the issue of NITRIFICATION is generally not well understood by many in the industry, both the causes of it, the management of it, or even why NITRIFICATION is of concern from a DRINKING water quality and public health perspective. This paper seeks to explain simply what NITRIFICATION is, its causes, its risks to DRINKING water quality and public health, and how it can be managed or prevented using examples from my work with water utilities across South Australia and Victoria. DISCUSSION Description of NITRIFICATION NITRIFICATION is the proliferation of nitrifying bacteria, microorganisms that oxidize free ammonia to nitrite and nitrate (Regan et.)

5 Al., 2002). Free ammonia is added to the CHLORAMINATED distribution systems as excess free ammonia from the formation of chloramines and also that which is released from chloramine decay. Ammonia oxidising bacteria (AOB) are able to feed on the free ammonia in the water producing nitrite. 77th WIOA Victorian water Industry Operations Conference & Exhibition Page No. 44 Bendigo Exhibition Centre, 2 to 4 September, 2014 Although it is suggested that a chemical reaction between chloramines and nitrite may lead to the formation of more free ammonia and nitrate it is acknowledged that a community of nitrite oxidising bacteria (NOB) along with AOB will favour the biological oxidation of nitrite to nitrate by NOB (Regan et.

6 Al., 2002). The proliferation of each of these microorganisms leads to often rapid depletion of chloramine residuals and the development of a microbial community in the distribution system and deterioration of DRINKING water quality. This is often observed as an increase in heterotrophic plate counts and coliform detections (Regan et. al., 2002). Although NITRIFICATION does not have direct impacts on public health, it is still an important process to control and ensure does not take control across distribution systems. This is primarily because NITRIFICATION leads to a rapid loss of chloramine residuals which are an important barrier in the management and protection of water quality in distribution systems.

7 The loss of chloramine residual leaves the distribution system susceptible to microbiological contamination with potential public health implications. Causes of NITRIFICATION There are a number of different factors which have been identified as contributing to the proliferation of AOB and NOB in CHLORAMINATED DRINKING water supplies. These factors include high free ammonia, water temperature >15 C, low chlorine residual (<2 mg/L), low pH, and high water age. Vikesland et al. (2001) highlights that while higher free ammonia will favour NITRIFICATION by providing ammonia for the AOB, higher free ammonia will also promote the formation of more stable chloramines. This highlights the need to get the chlorine to ammonia dosing ratio at an appropriate level at the treatment plant so that there is only a small amount of free ammonia remaining in the water following the formation of chloramines.

8 NITRIFICATION is known to be more likely to occur in distribution systems where the chloramine residual is <2 mg/L (US EPA, 2002). This is likely because higher chloramine residuals enable better control of microorganisms in the water . But nitrite produced by AOB may also accelerate the decomposition of monochloramine leading to further degradation of chloramine residuals (WHO, 2004). Thus as AOB begin to proliferate, a more rapid decay of chloramine residual is to be expected. Since chloramine residual typically decays over time as it is consumed gradually as a disinfectant, lower residuals are typically experienced where the water age is significant leading to higher risks of NITRIFICATION occurring.

9 High water age also typically occurs in areas where there is minimal movement of water such as in tanks and dead end mains. In addition slow movement of water and sediment build-up may also encourage the growth of microbiological communities. While lower pH may contribute to the viability of nitrifying bacteria, lower pH will also decrease the stability of chloramines and increase the rate of chloramine decay leading to lower chloramine residuals. Higher water temperatures are also known to increase the growth rate of nitrifying bacteria thus increasing the likelihood of NITRIFICATION occurring (US EPA, 2002). 77th WIOA Victorian water Industry Operations Conference & Exhibition Page No. 45 Bendigo Exhibition Centre, 2 to 4 September, 2014 Identification of NITRIFICATION The first challenge in management of NITRIFICATION is being able to identify when it has occurred or is likely to occur.

10 NITRIFICATION is able to be identified through careful monitoring of trends of various water quality parameters. The parameters which should be monitored when seeking to identify instances of NITRIFICATION are free ammonia, nitrite, nitrate and total chlorine. AOB will feed on free ammonia leading to a loss of free ammonia producing nitrite and an increasing nitrite trend. NOB feed on increasing levels of nitrite leading to an increasing nitrate trend. As AOB and NOB increase chlorine residuals are depleted very quickly. The loss of chlorine residuals is then often accompanied by increasing standard plate counts and detections of coliforms and E. coli. The changes are often rapid, with complete loss of chlorine residuals sometimes occurring with one to two weeks.